It is the goal of these investigations to elucidate the role of pulmonary mechanoreceptors and pulmonary chemoreceptors in the control of respiration. Of particular interest are the mechanisms underlying the respiratory center's use of information from pulmonary stretch receptors in regulating rate and depth of breathing. Computer techniques will be utilized in analyzing data from studies in anesthetized cats and dogs. I propose to use a technique for selective, reversible blockade of pulmonary receptors by inhalation of an aerosolized solution of local anesthetic to study the consequences of pulmonary stretch receptor blockade in the ventilatory responses to CO2 inhalation. An experimental preparation designed to uncouple the discharge from pulmonary stretch receptors from the central respiratory cycle will enable description of the effects of progressive increase in pulmonary stretch receptor activity on the rate and depth of breathing. This preparation is also suitable for the study of the response characteristics of a recently reported pulmonary CO2-sensitive receptor. A mechanistic view of the control of rate and depth of breathing suggests that there is some feature of the afferent discharge from pulmonary stretch receptors which the respiratory center utilizes in chosing a particular rate and depth at a given level of chemoreceptive demand. The predicted impulse traffic for spontaneous f and V sub T will be compared with that for experimentally controlled f and V sub T resulting in the same PaCO2 to determine if a unique feature of the ascending discharge operates at the spontaneous f and V sub T. We hope that an understanding of these physiological interactions will lead toward a fuller appreciation of the mechanisms of ventilatory control.